Fear turned to desperation on Sunday as hundreds of survivors fought over food and water in the cities worst affected by Chile’s devastating earthquake at the weekend, which killed at least 700 people.

Chilean television showed police firing tear gas canisters and water cannon at a crowd in Concepción, Chile’s second-biggest city and the one closest to the epicentre of the 8.8 magnitude quake – one of the most powerful ever recorded. The crowd smashed windows and clambered into a shop, dragging out sacks of rice, cartons of milk, bread and babies’ nappies.

Elsewhere, rescue workers tore through crashed masonry with shovels and sledgehammers, searching for survivors buried in the rubble of their homes. Some streets were littered with downed power lines, upturned cars and flattened traffic lights.

State television reported that 350 people had been killed in the southern fishing port of Constitución, which was also hit by a tsunami.

Michelle Bachelet, president, put the death toll at 708. She said the catastrophe was “enormous . . . there are a growing number of people unaccounted for, and this figure probably will continue to grow”.

In the port of Talcahuano, the centre of Chile’s fishing industry, around 25 boats were washed up into the city by powerful waves triggered by Saturday’s earthquake.

Rescue workers were trying to reach between 60 and 80 people thought to be trapped in an apartment block which had simply crumpled. Bridges collapsed, roads were buckled and aerial pictures showed desolate images of houses in coastal areas reduced to matchsticks and swathes of mangled rubble.

The government said some 2m people, an eighth of the population, have been directly affected by the quake, and around half a million houses were made uninhabitable. Ms Bachelet was closeted with officials on Sunday assessing how to respond.

Hillary Clinton, the US secretary of state, is due to visit Chile on Tuesday, and pledged to “provide necessary assistance to Chile in the days and weeks ahead”. Her visit will consist of meetings with Ms Bachelet and President-elect Sebastián Piñera at the airport.

Most of Chile’s copper mines, its biggest industry, were unaffected by the quake because they are in the north of the country but one of the country’s biggest ports was closed and wine regions near the epicentre preparing for this year’s harvest suffered.

The government has not yet put a figure on the rebuilding effort, but it will pose a challenge for Sebastián Piñera, who is who is to be sworn in as president on March 11. He has visited the affected areas, which the government has declared a catastrophe zone to speed up disbursement of aid.

About a fifth of the 6m population of Concepción remained without electricity and many lacked running water as aftershocks continued to scare survivors of the earthquake, which struck shortly after 3.30 a.m. on Saturday when most of the country was asleep.

Fuel is in short supply in the worst-hit areas and was being restricted to use in emergency vehicles only. The price of bread has shot up five-fold as supplies start to dwindle in the south. Firemen supplied survivors with water direct from their fire engines and long queues formed.